1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming system, and more particularly, to an image forming system for binding sheets already subjected to image formation together without using staples.
2. Description of the Related Art
Up to now, as an image forming apparatus, such as a copier, a laser beam printer, a facsimile machine, or a multifunction peripheral thereof and an image forming system including the image forming apparatus, there is an image forming system which includes a sheet processing apparatus for performing processing such as binding for sheets on which images are formed. In the image forming system, a sheet bundle is bound by the sheet processing apparatus generally by using metal staples. Staple processing using the staples allows multiple sheets of output paper to be reliably bound together in a position designated by a user, and is therefore employed by a large number of sheet processing apparatuses.
In the staple processing using the metal staples, the sheet bundle can be bound reliably, but when the sheet bundle that has been bound once is released, damage is highly likely to be done to the sheets even with special tools, and it is difficult to maintain quality of the sheets. The staples are consumables, and hence cost thereof is required.
In shredding the sheets subjected to the staple processing, the staples need to be removed, which requires time and labor. When recycling the sheet bundle bound by using the staples, it is necessary from the viewpoint of environmental issues to remove the staples and collect the sheets and the staples separately from each other, which also requires time and labor. The staples are disposed of after their use, resulting in waste of resources.
Among conventional sheet processing apparatus, there is proposed a sheet processing apparatus for binding sheets together without using staples by placing importance on recyclability in consideration of the environment and the like. As an example of the above-mentioned sheet processing apparatus, Japanese Patent Application Laid-Open No. 2010-189101 discloses a sheet processing apparatus for subjecting a sheet bundle to binding processing by using a binding portion provided with upper teeth and lower teeth each having a concave and convex portion.
In the above-mentioned sheet processing apparatus, after sheets are stacked and aligned, the lower teeth and the upper teeth of the binding portion are engaged with each other to form depth-direction asperities in a part of the sheet bundle, thereby fibers of the overlapping sheets of the sheet bundle are entangled with each other to bind the sheet bundle. In other words, according to the above-mentioned sheet processing apparatus, fibrous sheets are bound together without using staples. Such a binding method of binding a bundle of fibrous sheets without using staples is hereinafter referred to as “stapleless binding”.
In cases of a conventional image forming apparatus and a conventional image forming system which include the sheet processing apparatus for binding the sheet bundle by entangling the fibers of the sheets with each other, the binding of the sheets is affected by toner images formed on the sheets. For example, in a case where the toner images are formed on surfaces of the sheets that are brought into contact with each other, sheet surfaces are covered with toner, and hence the fibers of the sheets are hard to be entangled with each other. In other words, depending on a ratio of the toner covering the sheet surface within a region in which binding is to be performed, the sheet bundle cannot be bound even by being depressed in a teeth shape because the fibers of the sheets fail to be entangled with each other.
The present invention has been made in view of the above-mentioned circumstances, and provides an image forming apparatus and an image forming system which are capable of reliably subjecting sheets to stapleless binding.